The EfeB structure complexed with heme in PDB:3O72 is derived from E. coli O157 but differs from K-12 EfeB by only one residue, F416L (Liu, 2011). The acquisition of iron from exogenous heme when the foreign heme receptor HasR is expressed is reduced in an efeB or yfeX single mutant and eliminated in an efeB yfeX double mutant; overproduced EfeB complements a yfeX mutation, indicating some cytoplasmic activity of EfeB; the Dpp dipeptide/heme permease is required since the utilization of iron extracted from heme by EfeB in the periplasm requires an active EfeUOB iron transporter; iron is extracted without rupturing the tetrapyyrol ring; EfeB and YfeX facilitate the conversion of heme to protoporphyrin IX (PPIX) (Letoffe, 2009). The EfeUOB tripartite iron transporter is silent in E. coli K-12 due to a mutation in EfeU (Cao, 2007). False positive lipoprotein prediction, Cys not conserved. Verified Tat substrate: EfeB has a Tat/Sec (Class II) 35 aa signal peptide (Tullman-Ercek, 2007). The first 35 aa of EfeB have been confirmed as a type I signal peptide by electrospray MS of the intact periplasmic protein (Sturm, 2006). efeUOB of K-12 are transcribed as an iron-depletion-inducible, Fur-dependent operon (McHugh, 2003; Grosse, 2006). yfeX and efeB are paralogs and representatives of the DyP-type peroxidase family.